Osteoporosis is a condition of excessive skeletal fragility which is manifest as atraumatic or low-trauma fractures in elderly women and, to a lesser extent, men. It is extremely common, even epidemic, as judged by the very high incidence and prevalence of fractures among the elderly. This project proposes to study the epidemiology of skeletal fragility in a.properly chosen population and to determine the propensity to fracture among members of that population. The epidemiology of skeletal fragility is distinct from the epidemiology of fractures, because persons with increased skeletal fragility do not always have fractures. Those without fractures represent a reservoir of undetected osteoporosis in the population. We now have the tools to study the epidemiology of skeletal fragility and this application proposes to do so. The specific aims are: 1) to enumerate the entire population of non-institutionalized persons 50 years of age and older in Saunders County, Nebraska, 2) to determine the distribution of values for two measures of bone strength/fragility, Apparent Velocity of Ultrasound (AVU) of the patella, and Single Photon Absorptiometry (SPA) of the forearm, in a sample from the population enumerated in Aim #1, and 3) to conduct a four-year, prospective study of the sample recruited in Aim #2 to assess the risk of vertebral and appendicular fracture as a function of skeletal fragility. The hypotheses to be tested are: 1) Skeletal fragility can be assessed in a population of persons aged 50 years and older by measuring AVU of the patella and bone mass of the forearm by SPA, and 2) Skeletal fragility, as detected by AVU and SPA, is related to the risk of low-trauma fracture.